The present invention relates to a control apparatus for a cylinder injection type internal combustion engine that switches the fuel injection mode of the engine between a compression stroke injection and an intake stroke injection.
Fuel is directly injected from a fuel injection valve to a combustion chamber in the cylinder injection type internal combustion engine. In this type of internal combustion engine, fuel is injected at the final stage of the compression stroke of a piston, during which the piston approaches the fuel injection valve. Therefore, the injected fuel collides with the top surface of the piston. As a result, the injected fuel is directed toward a spark plug. This is disclosed in Japanese Unexamined Patent Publication No. 4-187841.
The compression stroke injection allows air-fuel mixture having a high fuel concentration to be formed in the vicinity of the spark plugs and to be burned. This is called stratified charge combustion. Therefore, even when the average fuel concentration of the air-fuel mixture is set low, or the ratio of air to fuel is relatively high, stable combustion is obtained.
The typical internal combustion engine including the cylinder injection type internal combustion engine is provided with a catalyst converter (hereinafter, simply referred to as catalyst) in an exhaust system. Unburned components such as hydrocarbons included in the emission gas are purified by the oxidation-reduction reaction of the catalyst. However, the emission purification performance of the catalyst tends to decrease when the bed temperature of the catalyst is not increased enough due to a low temperature of the emission gas, for example, when the engine is cold.
Therefore, for the cylinder injection type internal combustion engine, the compression stroke injection is selected for the fuel injection mode when the engine is cold. Then, stratified charge combustion is executed. When the compression stroke injection is executed while the engine is cold, the fuel concentration of the air-fuel mixture is low, which reduces the emission of unburned component. Therefore, even when the emission purification performance of the catalyst is decreased, the deterioration of emission quality due to the emission of unburned component is suppressed.
When the fuel injection amount increases, according to the increase of the engine load, the fuel concentration of the air-fuel mixture in the vicinity of the spark plugs increases. In this state, to avoid misfires, the compression stroke injection is not executed. Therefore, when the compression stroke injection is not allowed because of, for example, a great engine load, the fuel injection mode is switched from the compression stroke injection to the intake stroke injection.
However, when the fuel injection mode is switched from the compression stroke injection to the intake stroke injection while the engine is cold, the following problems occur. During the compression stroke injection, the fuel is injected against the top surface of the piston. Therefore, the fuel adheres to the top surface of the piston. When the engine is cold, the top surface of the piston tends to be cold and the adhered fuel resists vaporization. Accordingly, the amount of fuel that adheres to the top surface of the piston gradually increases. If the fuel injection mode is switched from compression stroke injection to intake stroke injection when the amount of adhered fuel is increased, the adhered fuel vaporizes by the combustion heat during, for example, the exhaust stroke after the air-fuel mixture is combusted. Thus, some of the vaporized fuel is exhausted as unburned discharge gas. Particularly, during the execution of intake stroke injection while the engine is cold, the air-fuel mixture needs to have a high fuel concentration to stabilize combustion. Therefore, the amount of unburned discharge gas contained in the emission gas increases accordingly. Therefore, when the fuel injection mode is switched, the amount of unburned discharge gas increases temporarily and the deterioration of the emission quality, such as the occurrence of black smoke, cannot be avoided.
The objective of the present invention is to provide a control apparatus that suppresses deterioration of the emission quality due to an increase of the amount of the unburned discharge gas that is caused when the fuel injection mode is switched from the compression stroke injection to the intake stroke injection.
To achieve the foregoing objective, the present invention provides a control apparatus for a cylinder injection type internal combustion engine. The fuel injection mode of the engine is switched between a compression stroke injection and an intake stroke injection. When the engine is cold, the compression stroke injection is selected for the injection mode so that injected fuel collides with the top surface of a piston and is directed toward the vicinity of a spark plug. The control apparatus includes a delay correction means. When the fuel injection mode is switched from the compression stroke injection to the intake stroke injection, the delay correction means delays the ignition timing during the execution of the intake stroke injection from when the fuel injection mode is switched until a predetermined period elapses compared with a case when the fuel injection mode is not switched.
The present invention also provides a control apparatus for a cylinder injection type internal combustion engine. The fuel injection mode of the engine is switched between a compression stroke injection and an intake stroke injection. When the engine is cold, the compression stroke injection is selected for the injection mode so that injected fuel collides with the top surface of a piston and is directed toward the vicinity of a spark plug. The control apparatus includes decrease correction means and determining means. When the fuel injection mode is switched from the compression stroke injection to the intake stroke injection, the decrease correction means decreases the fuel injection amount during the execution of the intake stroke injection from when the fuel injection mode is switched until a predetermined period elapses. Based on the condition of the engine when the compression stroke injection is selected for the fuel injection mode, the determining means estimates the amount of fuel adhered on the top surface of the piston at time when the fuel injection mode is switched from the compression stroke injection to the intake stroke injection. The determining means determines whether the estimated adhered fuel amount is greater than or equal to a predetermined amount. If the determining means determines that the estimated adhered fuel is greater than or equal to the predetermined amount, the decrease correction means executes decrease correction of the fuel injection amount.
The present invention also provides a control apparatus for a cylinder injection type internal combustion engine. The fuel injection mode of the engine is switched between a compression stroke injection and an intake stroke injection. When the engine is cold, the compression stroke injection is selected for the injection mode so that injected fuel collides with the top surface of a piston and is directed toward the vicinity of a spark plug. The control apparatus includes decrease correction means and setting means. When the fuel injection mode is switched from the compression stroke injection to the intake stroke injection, the decrease means decreases the fuel injection amount during the execution of the intake stroke injection from when the fuel injection mode is switched until a predetermined period elapses compared with a case when the fuel injection mode is not switched. Based on the condition of the engine during the execution of the compression stroke injection, the setting means estimates the amount of fuel adhered on the top surface of the piston at the time when the fuel injection mode is switched from the compression stroke injection to the intake stroke injection. The setting means extends the predetermined period as the estimated adhered fuel amount increases.
A further aspect of the present invention is a control method for a cylinder injection type internal combustion engine. The fuel injection mode of the engine is switched between a compression stroke injection and an intake stroke injection. When the engine is cold, the compression stroke injection is selected so that injected fuel collides with the top surface of a piston and is directed toward the vicinity of a spark plug. The control method includes when the fuel injection mode is switched from the compression stroke injection to the intake stroke injection, delaying the ignition timing during the execution of the intake stroke injection from when the fuel injection mode is switched until a predetermined period elapses compared with a case when the fuel injection modes are not switched.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.